1. Field of the Invention
This invention relates to a microscope objective applicable to a microscope or microscope system with high extensiveness that provides a large numerical aperture to realize acquisition of a feeble luminous signal at a high S/N ratio in microscopy while having a wide observation range.
To be specific, this invention relates to a microscope objective that provides a wide observation range, a large entrance-side numerical aperture. NA to assure a high resolution, a large exit-side numerical aperture NA′ to realize acquisition of a feeble luminous signal at a high S/N ratio, and a good aberration performance.
2. Description of Related Art
In the most advanced research field at present, various methods of observing cells, in vivo, for a long period of time (several days to several weeks) are developed for purposes of the functional clarification of living cells and the behavior analysis and interaction clarification of a protein. As one technique of microscopy for observing a lesion part inside living cells, the method of making a fluorescence observation is largely used. The fluorescence observation is such that, after a particular fluorescent substance like a fluorescent protein is used as a light-emitting label to stain a living specimen like living cells, fluorescent light is produced by irradiation of the specimen with exciting light and is observed to thereby detect the existence and position of a particular part in the living specimen, such as a lesion part inside the living cells.
In the fluorescence observation, when some stimulus is given to the living specimen, for example, by irradiation with exciting light, there is a possibility that the stimulus itself adversely affects an active state of the cell. Consequently, it is desired to provide a microscope system such that the light-emitting label is stimulated with the weakest possible stimulus (low-intensity exciting light) and a weak luminous signal produced in accordance with this stimulus can be detected at extremely high efficiency.
Simultaneously, it is also desired to provide a microscope system in which provisions are made for keeping a state of behavior of the living cell in sight and at the same time, detecting much information from the cell at a time through the observation in a wide range so that a processing speed and work efficiency can be improved.
In general, an objective for biological microscopes is constructed so that an observation object (the specimen) is viewed through a cover glass and is designed so that, for example, aberrations produced by the cover glass are corrected on the premise that the thickness of the cover glass has a constant reference value.
However, the cover glass is attended with a fabrication error. Depending on the observation technique, the observation object is sometimes viewed through a nearly plane-parallel plate such as a cover glass of thickness different from that of the reference value or a Petri dish.
Thus, when the thickness of the cover glass is varied to differ from that of the reference value, aberrations produced in accordance with variation of the thickness of the cover glass cannot be completely compensated for by the objective and imaging performance is degraded. In particular, as the numerical aperture NA becomes high, the degradation of the imaging performance becomes pronounced.
Conventional microscope objectives for compensating for aberrations produced in accordance with the variation of the thickness of the cover glass interposed between the surface of the observation object and the objective are set forth, for example, in Japanese Patent Kokai No. Hei 03-58492 and Japanese Patent No. 3371934.
In the field of conventional microscope apparatuses, however, microscope apparatuses fulfilling the above requirements and microscope systems provided with these microscope apparatuses have no existence. As such, the objectives set forth in the prior art references mentioned above are not constructed on the premise that they are applied to microscope apparatuses fulfilling the above requirements and microscope systems provided with these microscope apparatuses.
In this regard, the applicant of the present invention, in Japanese Patent Kokai No. 2007-41510 filed by this applicant, has proposed a microscope fulfilling the above requirements, that is, a microscope with high extensiveness that provides a large numerical aperture to realize acquisition of a feeble luminous signal at a high S/N ratio while having a wide observation range, and a microscope system provided with such a microscope.
Even in such a microscope objective, it is desired to correct aberrations produced in accordance with variation of the thickness of the cover glass. In biochemical microscopy, the fluctuation of aberrations may be caused not only by variation of the thickness of the cover glass, but also by a difference with room temperature in the case where the microscope is used at the temperature of cell culture, and correction of the fluctuation of aberrations is desired.
To be more specific, what is required for the above-mentioned microscope system optimized for fluorescence observation of living specimen is a microscope objective having a wide observation range, a large entrance-side numerical aperture NA, a large exit-side numerical aperture NA′, and a good aberration performance.
Conventional microscope objectives having a wide observation range, a large exit-side numerical aperture NA′ and a good aberration performance are set forth, for example, in:
Japanese Patent Kokai No. 2001-21812, which discloses an objective of dry type with magnification β=2×, focal length f=90 mm, total length Dt=69 mm, entrance-side numerical aperture NA=0.13 and exit-side numerical aperture NA′=0.65;
Japanese Patent Kokai No. Hei 11-231224, which discloses an objective of dry type with magnification β=4×, focal length f=45 mm, total length Dt=66.8 mm, entrance-side numerical aperture NA=0.267 and exit-side numerical aperture NA′=0.06675;
U.S. Pat. No. 5,920,432, which discloses an objective of dry type with magnification β=10×, focal length f=20 mm, total length Dt=63.2 mm, entrance-side numerical aperture NA=0.5 and exit-side numerical aperture NA′=0.05, and an objective of dry type with magnification β=20×, focal length f=10 mm, total length Dt=61.7 mm, entrance-side numerical aperture NA=0.75 and exit-side numerical aperture NA′=0.038;
Japanese Patent Kokai No. 2005-189732, which discloses an objective of water immersion type with magnification β=1.6×, focal length f=12.5 mm, total length Dt=79.4˜91.6 mm, entrance-side numerical aperture NA=0.8 and exit-side numerical aperture NA′=0.05;
U.S. Pat. No. 6,501,603 B2, which discloses an objective of dry type with magnification β=20×, focal length f=9 mm, total length Dt=72.9 mm, entrance-side numerical aperture NA=0.8 and exit-side numerical aperture NA′=0.04; and an objective of water immersion type with magnification β=20×, focal length f=9 mm, total length Dt=79.5˜80.3 mm, entrance-side numerical aperture NA=0.9˜0.94 and exit-side numerical aperture NA′=0.045˜0.047;
Japanese Patent Kokai No. 2007-133071, which discloses an objective of oil immersion type with magnification β=20×, focal length f=10 mm, total length Dt=60.2˜62.4 mm, entrance-side numerical aperture NA=0.95 and exit-side numerical aperture NA′=0.0475; and
U.S. Pat. No. 7,382,542 B2, which discloses an objective of water immersion type with magnification β=20×, focal length f=8.2 mm, total length Dt=71.4˜78.5 mm, entrance-side numerical aperture NA=1.0 and exit-side numerical aperture NA′=0.05.